In industrial measurements technology—especially in connection with the control and monitoring of automated manufacturing processes—for ascertaining characteristic measured variables of flowing media (for example, liquids and/or gases) in a process line (for example, a pipeline), such measuring systems are often used, which, by means of a measuring transducer of vibration-type, and by means of transmitter electronics connected thereto and most often accommodated in a separate electronics housing, induce in the flowing medium reaction forces (for example, Coriolis forces) and, derived from these, recurrently produce measuring values correspondingly representing the at least one measured variable, for example, a mass flow rate, a density, a viscosity or another process parameter. Such measuring systems—often formed by means of an in-line measuring device of compact construction with integrated measuring transducer, such as, for instance, a Coriolis-mass flow meter—are long known and have proved themselves in industrial use. Examples of such measuring systems with a measuring transducer of vibration type or also individual components thereof, are, for example, described in U.S. Pat. Nos. 4,680,974, 4,738,144, 4,768,384, 4,801,897, 4,823,614, 4,879,911, 5,009,109, 5,050,439, 5,359,881, 5,602,345, 5,734,112, 5,796,011, 5,926,096, 5,969,264, 7,127,952, 6,092,429, 6,311,136, 6,883,387, 7,325,461, 7,392,709, 7,421,350, WO-A 96/08697 or WO-A 2007/040468. The measuring transducers shown therein include, accommodated in a measuring transducer housing, at least two essentially straight or curved (e.g. U- or V-shaped) measuring tubes for conveying the (in given cases, also inhomogeneous, extremely hot or also very viscous) medium, wherein the at least two measuring tubes, forming a tube arrangement with flow paths connected in parallel to one another, are integrated into the process line via an inlet-side flow divider extending between the measuring tubes and an inlet-side connecting flange, as well as via an outlet-side flow divider extending between the measuring tubes and an outlet-side connecting flange. In measuring operation, the then parallelly flowed-through measuring tubes are caused to vibrate for the purpose of generating oscillation forms influenced by the medium flowing through.
In the case of measuring transducers with curved measuring tubes, usually selected as the excited oscillation form—the so-called wanted mode—is that eigenoscillation form, in the case of which each of the measuring tubes at least partially moves in a pendulum-like manner at a lowest natural resonance frequency about an imaginary longitudinal axis of the measuring transducer in the manner of cantilever clamped at one end, whereby Coriolis forces dependent on the mass flow are induced in the medium flowing through. These Coriolis forces, in turn, have the effect that, superimposed upon the excited oscillations of the wanted mode, in the case of curved measuring tubes, thus pendulum-like cantilever oscillations, are bending oscillations of a frequency equal therewith according to at least one likewise natural, second oscillation form, the so-called Coriolis mode. In the case of measuring transducers with curved measuring tubes, these cantilever oscillations in the Coriolis mode compelled by Coriolis forces, usually correspond to that eigenoscillation form, in the case of which the measuring tube also executes rotary oscillations about an imaginary vertical axis aligned perpendicular to the longitudinal axis. In the case of measuring transducers with straight measuring tubes, in contrast, for the purpose of producing Coriolis forces dependent on mass flow, such a wanted mode is often selected, in the case of which each of the measuring tubes at least partially executes bending oscillations essentially in a single imaginary plane of oscillation, such that the oscillations in the Coriolis mode accordingly are embodied as bending oscillations coplanar with the wanted mode oscillations, and having an equal oscillation frequency. For exciting oscillations of the at least two measuring tubes, measuring transducers of vibration-type additionally have an exciter mechanism driven during operation by an electrical driver signal (e.g. a controlled electrical current) which is generated and correspondingly conditioned by the mentioned driver electronics; wherein the exciter mechanism, by means of at least one electro-mechanical—especially electro-dynamic—oscillation exciter, which, during operation, is flowed through by an electrical current, and which acts practically directly, especially differentially, on the at least two measuring tubes, excites the measuring tube in the wanted mode to bending oscillations, especially opposite equal bending oscillations. Furthermore, such measuring transducers comprise a sensor arrangement with oscillation sensors, especially electro-dynamic, oscillation sensors for at least point registering inlet-side and outlet-side oscillations of at least one of the measuring tubes, especially opposite-equal bending oscillations of the measuring tubes in the Coriolis mode, and for producing electrical sensor signals, which are influenced by the process parameter to be registered (such as, for instance, the mass flow or the density), and which serve as vibration signals of the measuring transducer. As, for example, is described in U.S. Pat. No. 7,325,461, in the case of measuring transducers of the type being discussed, in given cases, the oscillation exciter can, at least at times, also be used as an oscillation sensor, and/or an oscillation sensor can at least at times be used as an oscillation exciter. The exciter mechanism of measuring transducers of the type being discussed usually includes at least one oscillation exciter, which is electrodynamic and/or acts differentially on the measuring tubes, while the sensor arrangement comprises an inlet-side, most often likewise electrodynamic, oscillation sensor, as well as at least one outlet-side oscillation sensor, which is essentially equally-constructed thereto. Such electrodynamic and/or differential oscillation exciters of measuring transducers of the vibration-type available on the market are formed by means of a magnet coil, through which an electrical current flows, at least at times, and which is affixed to one of the measuring tubes, as well as by means of a rather elongated, especially rod-shaped, permanent magnet, which interacts with the at least one magnet coil (especially plunging into this), and which serves as an armature, which is correspondingly affixed to the other measuring tube, which is to be moved in an opposite-equal manner. The permanent magnet and the magnet coil serving as the exciter coil are, in such case, usually oriented in such a way, that they essentially extend coaxially to one another. Additionally, in the case of conventional measuring transducers, the exciter mechanism is usually embodied and placed in the measuring transducer in such a manner, that it in each case acts essentially centrally on the measuring tubes. In such case, the oscillation exciter and, to this extent, the exciter mechanism—as, for example, is also shown in the case of the proposed measuring transducers—is externally affixed to the measuring tubes at least pointwise along an imaginary central peripheral line of each. As is, among other things, described in U.S. Pat. No. 6,092,429 or U.S. Pat. No. 4,823,614, as an alternative to an exciter mechanism formed by means of oscillation exciters acting rather centrally and directly on the measuring tubes, exciter mechanisms formed by means of two oscillation exciters affixed, in each case, not at the half-lengths of the measuring tubes, but rather on the inlet, or on the outlet, sides thereof can, for example, also be used. In the case of most measuring transducers of vibration-type available on the market, the oscillation sensors of the sensor arrangement are embodied so as to be essentially of equal construction to the at least one oscillation exciter, at least insofar as they work according to the same principle of action. Accordingly, the oscillation sensors of such a sensor arrangement also are, in each case, most often formed by means of at least one coil affixed to one of the measuring tubes, which is at least at times passed through by a variable magnetic field and, in association therewith, at least at times supplied with an induced measurement voltage, as well as by means of a permanently magnetic armature, which is affixed to another of the measuring tubes, which interacts with the at least one coil, and which delivers the magnetic field. Each of the aforementioned coils is additionally connected with the aforementioned transmitter electronics of the in-line measuring device by means of at least one pair of electrical connecting lines, which most often extend along as short a path as possible from the coils to the measuring transducer housing. Due to the superpositioning of the wanted and Coriolis modes, the oscillations of the vibrating measuring tubes registered by means of the sensor arrangement on the inlet side and on the outlet side also have a measurable phase difference, dependent on the mass flow. Usually, the measuring tubes of such (e.g. applied in Coriolis-mass flow meters) measuring transducers are, during operation, excited to an instantaneous natural resonance frequency of the oscillation form selected for the wanted mode, e.g. at a constant, controlled oscillation amplitude. Since this resonance frequency is also especially dependent on the instantaneous density of the medium, besides the mass flow, the density of flowing media can also additionally be measured by means of Coriolis mass flow meters typically available on the market. Additionally, as, for example, is shown in U.S. Pat. No. 6,651,513 or U.S. Pat. No. 7,080,564, it is also possible by means of measuring transducers of vibration-type directly to measure viscosity of the medium flowing through, for example, based on an exciter energy or excitation power required for maintaining the oscillations, and/or based on a damping of oscillations (especially those in the aforementioned wanted mode) of the at least one measuring tube, resulting from a dissipation of oscillatory energy. Moreover, other measured variables derived from the aforementioned primary measured values of mass flow rate, density and viscosity can also be ascertained, such as, for instance, the Reynolds number according to U.S. Pat. No. 6,513,393.
Especially in the case of application of measuring systems of the aforementioned type for measuring high viscosity (for example pasty, doughy or slurry-like) media, or also for measuring of media, in the case of which are conveyed solids with diameters in the order of magnitude of a caliber of a measuring tube, such as, for example, stone-containing slurries, concrete, fruit sauces (such as apple sauce), etc., an increased risk exists that one of the measuring tubes becomes partially or completely plugged, for example, as a result of a solid jammed in one of the measuring tubes, while the other of the measuring tubes is still flowed through by the medium. As a result of such a partial plugging of the tube arrangement, the measuring transducer is, without such being recognized, now flowed through only asymmetrically; in given cases, also in such a manner, that the medium flows only in one of the measuring tubes, or one of the measuring tubes is no longer flowed through. However, with conventional measuring systems of the type being discussed, such an asymmetric flow through the measuring transducer or a partial plugging of the tube arrangement causing this is, in measuring operation—here, thus, with medium flowing through the measuring transducer and measuring tubes oscillating in the wanted mode—not, at present, detectable, nor has any attempt at all been made to detect such. In the previously mentioned U.S. Pat. No. 7,421,350, a method has been provided for detection of media residues remaining in the measuring transducer after its emptying, which can correspondingly also be used for detection of plugging, wherein, on the basis of an exceeding of a limit value set, in the case of an emptied measuring system, for an oscillation parameter derived for one of the vibration signals (e.g. a resonance frequency of the wanted mode), it is detected whether or not medium is nevertheless still in the measuring transducer after the measuring system is thought to have been emptied; however, an application of said method for flowed-through measuring systems is not directly possible, because an exceeding of the aforementioned limit value can also be attributed solely to a significant change of properties of the medium, such as, for instance, the density and/or the viscosity. Also, the phase shift between the vibration-signals typically measured in measuring systems of the aforementioned type is not a reliable indicator for a partial plugging of the measuring transducer, because the at least one measuring tube still flowed through furthermore also oscillates in the Coriolis mode, and, thus, the vibration signals produced by means of the sensor arrangement are still phase shifted with respect to one another.
Since it is—at least in the case of applications, for instance, in the pharmaceuticals industry or the foods industry, not least of all for hygienic reasons—however, quite desirable, to also be able to detect and correspondingly signal a partial plugging during running measurement operation both reliably and an as early as possible (for instance, directly after occurrence), an object of the invention is to provide a method for monitoring a tube arrangement having at least two measuring tubes which, during operation, are flowed through in parallel by the medium; especially a method for detecting a plugging even of only one of the measuring tubes of said tube arrangement; as well as a measuring arrangement for this method.
For achieving the object, the invention resides in a method for monitoring a tube arrangement formed by means of a first measuring tube and at least a second measuring tube, which connected for parallel flow with the first, wherein the method comprises steps as follows:                Permitting medium to flow through the tube arrangement;        ascertaining a temperature difference existing between the first measuring tube and the second measuring tube; and        signaling a partial plugging of the tube arrangement, for example a plugging of exactly one of the measuring tubes and/or a plugging of the first measuring tube, in the case of a simultaneously non-plugged, second measuring tube, if the ascertained temperature difference deviates from a predetermined limit value representing the temperature difference of a non-plugged tube arrangement.        
Moreover, the invention resides in a measuring system (for example, embodied as a compact measuring device and/or as a Coriolis mass flow-measuring device) for a medium flowing through a pipeline—for example, an aqueous liquid, a slurry, a paste or other flowable material—wherein the measuring system (which is, for example, embodied as a compact measuring device and/or as a Coriolis mass flow measuring device) comprises: A measuring transducer (through which the medium flows during operation) for producing vibration signals corresponding with parameters of the flowing medium, for example a mass flow rate, a density and/or a viscosity; as well as a transmitter electronics electrically coupled with the measuring transducer for activating the measuring transducer and for evaluating measuring signals delivered by the measuring transducer; wherein the measuring transducer has an inlet-side, first flow divider with at least two flow openings which are spaced apart from one another, an outlet-side, second flow divider with at least two flow openings which are spaced apart from one another, at least two measuring tubes connected to the flow dividers, especially equally constructed flow dividers, for forming a tube arrangement having at least two flow paths connected for conveying flowing medium with parallel flow, of which a first measuring tube opens with an inlet-side first measuring tube end into a first flow opening of the first flow divider and with an outlet-side second measuring tube end into a first flow opening of the second flow divider; and a second measuring tube opens with an inlet-side first measuring tube end into a second flow opening of the first flow divider and with an outlet-side second measuring tube end into a second flow opening of the second flow divider; wherein the measuring system, for monitoring the tube arrangement, also has a temperature measuring arrangement connected to the transmitter electronics, wherein the temperature measuring arrangement, for producing a temperature signal dependent on a temperature of the first measuring tube, has a first temperature sensor, especially a first temperature sensor affixed directly to the first measuring tube and/or formed as a resistance thermometer, and, for producing a temperature signal dependent on a temperature of the second measuring tube, has at least a second temperature sensor, especially a second temperature sensor affixed directly to the second measuring tube and/or formed as a resistance thermometer. Additionally, it is provided that the transmitter electronics, with application of the temperature signal produced by means of the first temperature sensor and the temperature signal produced by means of the second temperature sensor, for example, a second temperature sensor constructed essentially equally to the first temperature sensor, generates, at least at times, an alarm signaling a partial plugging of the tube arrangement, especially a plugging of exactly one of the measuring tubes and/or a plugging of the first measuring tube, in the case of simultaneously non-plugged, second measuring tube.
According to a first embodiment of the measuring system of the invention, it is additionally provided that the transmitter electronics, making use of the temperature signal produced by means of the first temperature sensor and of the temperature signal produced by means of the second temperature sensor (which is, for example, essentially equally constructed to the first temperature sensor), at least at times generates an alarm signaling a partial plugging of the tube arrangement, if the temperature signal produced by means of the first temperature sensor and the temperature signal produced by means of the second temperature sensor deviate from one another with regard to at least one signal parameter derived in each case therefrom, especially a temporal average value of a signal amplitude of each of the two temperature signals, a variation of a signal amplitude of each of the two temperature signals, a cross correlation of the two temperature signals or the like, in excess of a limit value correspondingly predetermined therefor.
According to a second embodiment of the measuring system of the invention, it is additionally provided that the transmitter electronics, making use of a temperature difference signal formed by means of the temperature signal produced by means of the first temperature sensor and of the temperature signal produced by means of the second temperature sensor, this temperature difference signal representing a temperature difference existing between the first measuring tube and the second measuring tube, generates an alarm signaling a partial plugging of the tube arrangement, if the temperature difference represented by the temperature difference signal deviates from a therefor predetermined limit value representing a non-plugged tube arrangement.
According to a third embodiment of the measuring system of the invention, it is additionally provided that the first temperature sensor and the second temperature sensor are embodied and placed in the measuring transducer in such a manner, that the first temperature sensor, for instance, reacts as equally rapidly with a change of its temperature signal to a change in the temperature of the first measuring tube as the second temperature sensor reacts with a change of its temperature signal to a change in the temperature the second measuring tube.
According to a fourth embodiment of the measuring system of the invention, it is additionally provided that the first temperature sensor and the second temperature sensor are embodied and placed in the measuring transducer in such a manner, that the temperature signal produced by means of the first temperature sensor is dependent predominantly on the temperature of the first measuring tube, and the temperature signal produced by means of the second temperature sensor is dependent predominantly on the temperature of the second measuring tube.
According to a fifth embodiment of the measuring system of the invention, it is additionally provided that the first temperature sensor and the second temperature sensor are embodied and placed in the measuring transducer in such a manner, that the temperature signal produced by means of the first temperature sensor is more closely correlated with the temperature of the first measuring tube than the temperature signal produced by means of the second temperature sensor.
According to a sixth embodiment of the measuring system of the invention, it is additionally provided that the first temperature sensor and the second temperature sensor are embodied and placed in the measuring transducer in such a manner, that the temperature signal produced by means of the second temperature sensor is more closely correlated with the temperature of the second measuring tube than the temperature signal produced by means of the first temperature sensor.
According to a seventh embodiment of the measuring system of the invention, it is additionally provided that the transmitter electronics, making use of the temperature signal produced by means of the first temperature sensor and of the temperature signal produced by means of the second temperature sensor (which is, for example, essentially equally constructed to the first temperature sensor), at least at times produces a temperature measured value, which represents a temperature of the medium flowing in the tube arrangement, especially when the transmitter electronics do not detect a partial plugging of the tube arrangement.
According to an eight embodiment of the measuring system of the invention, it is additionally provided that the first temperature sensor is affixed to the first measuring tube, and/or that the second temperature sensor is affixed to the second measuring tube. Developing this embodiment of the invention further, it is additionally provided that, except for the first temperature sensor, no further temperature sensor is affixed to the first measuring tube, and/or that except for the second temperature sensor, no further temperature sensor is affixed to the second measuring tube.
According to a ninth embodiment of the measuring system of the invention, it is additionally provided that the measuring transducer has four measuring tubes for conveying the flowing medium, which, forming a tube arrangement with four flow paths, which are connected for parallel flow, are connected to, especially equally-constructed, flow dividers. Developing this embodiment of the invention further, it is additionally provided that the temperature measuring arrangement has a third temperature sensor for producing a temperature signal dependent on a temperature of a third measuring tube of the measuring transducer, and at least a fourth temperature sensor for producing a temperature signal dependent on a temperature of a fourth measuring tube of the measuring transducer.
According to a tenth embodiment of the measuring system of the invention, it is additionally provided that the measuring transducer further comprises a measuring transducer housing with an inlet-side first housing end, especially a first housing end having a connecting flange for a line segment conveying the medium to the measuring transducer and/or a first housing end formed by means of the first flow divider, and an outlet-side, second housing end, especially a second housing end having a connecting flange for a line segment conveying the medium away from the measuring transducer, and/or a second housing end formed by means of the second flow divider. Developing this embodiment of the invention further, it is additionally provided that the temperature measuring arrangement has, for producing a temperature signal dependent on a temperature of the measuring transducer housing, at least a third temperature sensor, which is especially affixed directly to the measuring transducer housing and/or embodied as a resistance thermometer. Making use of the temperature signal produced by the first temperature sensor as well as the temperature signal produced by the third temperature sensor, the transmitter electronics can then, for example, generate a report, which signals that the temperature signals delivered by the temperature measuring arrangement for monitoring the tube arrangement for partial plugging are suitable, insofar as a temperature of the medium in the measuring transducer deviates from a temperature of the measuring transducer housing; and/or the transmitter electronics can then, for example, generate a report, which signals that the temperature signals delivered by the temperature measuring arrangement for monitoring the tube arrangement for partial plugging are not instantaneously suitable, insofar as a temperature of the medium in the measuring transducer does not deviate or only deviates insufficiently from a temperature of the measuring transducer housing.
According to an eleventh embodiment of the measuring system of the invention, it is additionally provided that the measuring transducer further comprises at least one electro-mechanical, especially electrodynamic, oscillation exciter for exciting and/or maintaining vibrations of the at least two measuring tubes—especially of opposite equal bending oscillations of each of the at least two measuring tubes about an imaginary oscillation axis in each case imaginarily connecting an inlet-side, first measuring tube end of the particular measuring tube and an outlet-side, second measuring tube end of the particular measuring tube—with a natural resonance frequency of the measuring transducer.
According to a twelfth embodiment of the measuring system of the invention, it is additionally provided that the measuring transducer further comprises:                a first oscillation sensor, especially an electrodynamic one, for registering inlet-side vibrations of the at least two measuring tubes and for producing a first vibration signal of the measuring transducer representing vibrations of at least one of the measuring tubes, especially inlet-side vibrations of the first measuring tube relative to the second measuring tube; and        a second oscillation sensor, especially an electrodynamic one, for registering outlet-side vibrations of the at least two measuring tubes and for producing a second vibration signal of the measuring transducer representing vibrations of at least one of the measuring tubes, especially outlet-side vibrations of the first measuring tube relative to the second measuring tube. Developing this embodiment of the invention further, it is additionally provided that the transmitter electronics, making use of at least one of the vibration signals, generates an alarm signaling partial plugging of the tube arrangement, if said vibration signal deviates from a limit value correspondingly predetermined therefor with regard to at least one signal parameter in each case derived therefrom, especially a temporal average value of a signal amplitude, a variation of a signal amplitude, a signal frequency or the like. Moreover, the transmitter electronics can, however, by means of the first vibration signal and by means of the second vibration signal, also generate a phase difference measured value, which represents a phase difference existing between the first vibration signal and the second vibration signal, especially a phase difference dependent on a mass flow rate of the medium flowing in the measuring transducer, and/or generate a mass flow-measured value, which represents a mass flow rate of medium flowing in the measuring transducer.        
A basic idea of the invention is to use the heat flux regularly arising as a result of a partial plugging of pipe arrangements of the type being discussed between the plugged, no longer flowed-through tube and the non-plugged, still flowed-through measuring tube—or the temperature gradients resulting therefrom—as an indicator variable for monitoring the tube arrangement. The invention is based, among other things, on the recognition that, on the one hand, usually, in applications in industrial measuring and automation technology, media with a temperature deviating significantly from a surrounding temperature of the measuring system are to be measured, not least of all also during cleanings of such pipe arrangements regularly performed in the installed state by means of hot water or vapor; and that, on the other hand, in the case of pipe arrangements with measuring tubes parallelly flowed-through in undisturbed operation, in the case of a plugging of one of the measuring tubes, after a comparatively short time, a significant, very easily detected temperature difference relative to the other, still flowed-through measuring tube or a corresponding heat flux between measuring tubes of partially plugged pipe arrangements can already be detected.